Magnetic recording



Jan. 30, 1940. G. R. CLARK 2,188,650

MAGNETIC RECORDING Filed April 23, 1938 2 Sheets-Sheet l hm l 3| 4 Lia 2] 9 -24 i 23 26 INVENTOR.

ATTQRNEY.

Jan. 30, 1940. G. R. CLARK 2,188,650

MAGNETIC RECORDING Filed April 23, 1938 -2 Sheets-Sheet v2 I NV EN TOR.

/EERT R: CLARK yf www ATTORNEY.

Patented Jan. 3o, 1940 PATENT OFFICE MAGNETIC RECORDING Gilbert B. Clark, Brooklyn,

Ballo Corporation ol d Delaware N.Y..asaignorto corporatie mon Apl'll 23,1088, Serial No. 203,738

14 Claims. (Cl. 17a-100.2)

'Ihis invention relates to 'an improved system of magnetic recordingand reproducing of sound 'other signal impulse phenomena, particutoasystememployinsheet material as a agggga that the area of the sheet is progressively covered with a plurality of cmsswise strokes.

An object of this invention is to simplify and improve magnetic recording by employing a thin Isheet: of magnetic material;

Another object of this invention is to reduce g the speed of advance ormovement of the recording medium. leaving the rapid motion to a crosswise scanning between two spirals.

Still another object of this invention is to reduce tensional strains of magnetic material used I in recording for the reason that the sheet material employed is relatively wide and correspondstrong A further object of this invention is to increase the rewinding speed, thereby reducing the time dat! ln Plmn back.

A still further object of this invention is to provide a recording material which can be marked with suitable legends to indicate either the number of feet or minutes of playing time,

u which provides an accurate means of measuring and setting the sheet, which is an essential feature in many applications of sound recording.

Another object which is possible by the eni-A ployment of a wide sheet is that in addition to o sound recording, there can be provided a simple magnetic path at the edge of the sheet for a pilot carrier signal which may be employed to control the expansion or contraction of the signaling.

a Still another object of this invention is to enable the recording of soxmd of very high frequencies at a moderate cost.

Some of the features and advantages of this invention are as follows:

(a) '111e speed of advance is reduced considerably, leaving the rapid motion to a crosswise scanning between two spirals, which allows the sheet to be wound on a smaller diameter reel for a given playing time.

(b) Strainonthesheetisreducedascompared with strain on a wire or tape. Except for the component of sheet advance, strains are localized to the contact point between the two spirals, because the spirals are moving in opposite directions at this point. 5

(c) Because the sheet is wide, it is correspondingly strong; also, because of its width, it is not apt -to twist or tangle.

(d) 'Ihe rewinding speed can be very much faster than the recording speed, thereby reduc- .l0 ing delay in playing back.

(e) It"y enables recording and reproducing of very high frequencies at moderate cost.

(f) It is a practical method for extending the limit of continuous recording to covera very long interval of time.

(g) For applications where the sheet or belt must be fashioned into a continuous loop, it facilitates a long storage period before repetition.

(h) Markings can be made on the sheet proper to indicate either feet of tape, or minutes of playing time. This provides an accurate means of measuring and setting the sheet, a feature that is essential in many applications.

(i) Splices made in the sheet need not -have the same thickness or magnetic properties as the sheet, provided each splice is so located that the scanning does not occur along a splice, or include any part of it.

This invention will best be understood by referring to the accompanying drawings, in which:

Fig. l is a side elevation of an arrangement for magnetically recording on sheet magnetic material;

Fig. 2 isla plan view of Fig. l;

Fig. 3 is a longitudinal section of Figs. 1 and 2, the section being taken on line 3 3 of Fig. 2;

Pig. 3a is a developed detail of 4a. recording spiral shown in Fig. 3;

Fig. 4 is a perspective view showing a sheet of magnetic material, together with associated pilot recording and Wipeout elements;

Fig. 5 is a perspective detail view showing an arrangement of the Wipeout elements; and

Fig. 6 is a detail arrangement of a magnetic coupling with ball bearings.

Referring now in detail to the drawings, Figs. l and 2 show a sheet of magnetic material I, which is guided between two movable drums 2 and I by means oi sprockets 4 and 5 engaging in 50 a plurality of spacing holes 6 equally spaced along the margin of strip I.

The broken dash and dot lines la., shown also in Fig. 4, represent paths that are followed by successive scanning strokes, which paths have holes 8. The teeth on sprocket wheels I and 5 engage a spacing hole 6 on the sheet, and position the sheet correctly between a pair of spiral wires 'I and 8. These spirals are made by winding a magnetic wire on the surface of non-magnetic drums 2 and 3. The spirals are preferably wound on the drums with the same pitch and in the same direction so that at their points of contact with sheet I, they will cross each other. These drums are geared together by a system of gears 50 as shown in Fig. 1 to turn in the same direction and at the same angular velocity. Then,'providing the drums have been set so that the spirals cross exactly between the axis of the drums, thus contact will scan transversely across the sheetmaintaining the contact point directly between the two drums 2 and 3. The gear system 5|) is coupled to a constant speed electric motor, preferably to the shaft of .the center gear between drums 2 and 3.

Figs. 3 and 3a show in detail a schematic representation of the complete magnetic paths in which the ends of spirals 'l and 8 are shown connected with shafts I9 and 20 of drums 2 and 3, respectively. Numerals 2| and 22 indicate that part of each spiral wire where it leaves the drum surface and runsdirectly into the shaft of each drum. The magnetic path between spirals l and l follows the course marked between arrows I8 through sheet I, the magnetic circuit being completed through the external yoke 23 by way of bearings 2| and 25. A coil 26 is wound upon yoke 23 and is used for either recording or reproducing and is connected by means of leads 2l to a source of sound impulses or audio signals for recording, or to appropriate reproducing devices 40. The feed sprockets l and 5 which engage the feed holes 6 in the sheet must be geared to the drums so that the lines scanned when recording can be retraced when reproducing. The holes 6 should include a whole number of scanning lines between each aperture, that is, there should be either 1, 2, 3, 4, etc., scanning lines to each "of the said holes 6. This arrangement prevents the sheet from being located in an incorrect position on the feed sprocket wheel 4. As shown in Fig. 3a, the total overall length of the magnetic circuit remains constant, the two arrows indicating the point of contact, between spirals l and 8 through the sheet I.

The spirals l and 8 are exactly 360 or one y,

turn each. However, other than 360 spirals might be used, also in some applications it might be desirable to have a slight overlap. The magnetic circuit is arranged to provide a substantial constant reluctance of the magnetic path over the full length of each scanning stroke la. When adjacent scanning lines are far enough apart, splices in the sheet can be made between two scanning lines. On machines whose spirals are somewhat raised from the drum, points on the sheet and not on the scanning line may be somewhat thicker or thinner than the sheet. Therefore, splices can be made with a slight overlap, yet, this change in thickness will pass between the drums without jamming.

Fig. 4 shows how the sheet member of this invention can be advantageously employed to provide in addition to the scanning for the sound to be reproduced, a means to control the amplitude of the signal by the well-known expansion and contraction method employing a pilot carrier signal which may be located adjacent the apertureiandisindicatedinFig.4asadashand an integral numerical relation between the feed dot line 30. Also. if desired, a second signal can be recorded on the opposite marginal edge of sheet I, as shown by the dash and dot line 3|. Recording of pilot signal or signals 30 and Il is accomplished by means of the magnetic loops 5 29 and 32 which are surrounded by coils 26 and 3l, the coils being coupled to suitable apparatus for providing a suitable expansion and contraction medium.

As shown in Fig. 4, two magnetic bars Il and 34 are coupled to a coil 35 to uniformly magnetize the sheet before recording or when desired, to wipe out the signal after recording.

Fig. 5 shows another embodiment of Wipeout elements which tend towards keeping the Wipeout or magnetizing force constant across the sheet by having the magnetic circuit connected at opposite ends of bars 33 and N providing a substantially uniform field between the bars, which is an important feature as variations in reluctance of the magnetic circuit would effect the volume of the recording and when reproducing, this variation of reluctance further effects the volume in a cumulative manner.

Fig. 6 shows a detail of a modification in the magnetic path wherein collar type of ball bearings of suitable magnetic material form the magnetic path and connect to yoke 22, the ball bearings being located on the ends of the drum shafts.

Possible modifications include other systems of scanning. One method would be to curve the sheet, and scan with a toothed wheel. Another method would be to use a group of pointers on an endless belt, so arranged that one pointer would scan the sheet at a time. Still another method would be a single spiral in conjunction with a thin bar. Other possibilities with spirals on drums are:

More than a single spiral on one drum will provide multi-channel recording as scanning lines can be interspaced on the sheet.

Also, more than single spiral on both drums; or more than one complete turn for the spiral or spirals on either or both drums.

While only a few embodiments of this invention have been given, it is to be distinctly understood that it is capable of taking other forms. Furthermore, the arrangement makes magnetic recording more practical for the use of dictaphones, rebroadcasting, sound pictures, automatic collation, signal storage, and home recording, although its use should not be limited to these speciiic applications.

What is claimed is: u 1. A magnetic scanning system for recording signal impulses comprising a sheet of magnetic material, means for passing said sheet between a pair of movable drums having magnetic pickup means located thereon and to record a signal by magnetically coupling the movable elements with a source of signal impulses.

2. A magnetic scanning system for recording signal impulses comprising a sheet of magnetic material, means for passing said sheet between a pair of movable drums having a spiral path of magnetic wire in magnetic coupling with a source of signal impulses to magnetically record said signal impulses.

3. A magnetic scanning system for recording 'lo sound impulses comprising a long wide sheet of magnetic material having marginal apertures on each side thereof, and means for uniformly passing said sheet between movable members to re- 00rd sound by magnetically coupling the movable Il members with a source representative of said sound impulses.

4. A magnetic scanning system for recording sound impulses comprising a long wide sheet of magnetic material having marginal apertures on each side thereof, and means for uniformly passing said sheet between a pair of movable drums of non-magnetic material having magnetic pickup means located thereon, and means to record sound by magnetically coupling said pickup means on the movable drums with a source of electrical energy representative of said sound impulses.

5. A magnetic scanning system for recording sound impulses comprising a long wide sheet of ferro-magnetic material having marginal apertur on 'each side thereof, a plurality of sprockets engaging said apertures for uniformly passing said sheet between movable magnetic members and means to record the sound impulses by magnetically coupling the movable magnetic members with a source of electrical energy representative of said sound impulses.

v6. A magnetic scanning system for recording sound impulses comprising a long wide sheet of ferro-magnetic material having marginal apertures on each side thereof, a plurality of sprockets engaging said apertures for uniformly passing said sheet between a pair of movable drums of non-magnetic material, a spiral wire of magnetic material secured to each of said drums, and means to record the sound by magnetically coupling the spirals of the movable drums with a source of electrical energy representative of said sound impulses.

7.' A magnetic scanning system for recordingv sound impulses comprising a long wide sheet of magnetic material having marginal apertures on each side thereof, a plurality of sprockets engaging said apertures for uniformly passing said sheet between a pair of movable drums of nonmagnetic material, a spiral wire of magnetic material secured to each of said drums, and means to record the sound by magnetically coupling the spirals of the movable drums with electrical energy representativeof a source of sound. and a pair of magnetic bars arranged to magnetically wipe out said recorded sound impulses.

8. A magnetic scanning system for recording sound impulses comprising a sheet of ferro-magnetic material having marginal apertures thereon. means for passing said sheet between a pair of movable drum members having magnetic pickup means located thereon, said means comprising a plurality of sprockets engaging the marginal apertures on said sheet, and means for coupling said pickup means on the movable drum members with electrical energy representative ofamrceofsoundsaidmeanscomprisinga coilwhichisconnectedwithsaidsourceofelectrical energy representative of said sound im- 9.ailissneticscanuingsystemfcs'recordingr sound impulses comprising a sheet of ferromagnetic material, means for passing said sheet between movable magnetic members, means to record sound by magnetically coupling the movable members with electrical energy representative of said sound, and means for controlling the amplitude of said recorded sound, said means comprising a pilot signal which is magnetically coupled to Van apparatus' for expanding and contracting said sound impulses.

10. A magnetic scanning system for recording sound impulses comprisinga sheet of ferro-magnetic material, means for passing said sheet between movable magnetic members, means to record sound by magnetically coupling the movable members with electrical energy representative of said sound, and means for simultaneously controlling the amplitude of said recorded sound, said means comprising a pilot signal which is magnetically coupled to an apparatus for expanding and contracting said sound impulses.

11. A method of recording or reproducing sound by magnetic scanning including the step of drawing a strip of magnetic material through a magnetic field which is magnetically coupled through a plurality of ball bearings to a source of signals representative of sound impulses.

12. A magnetic scanning system for recording sound impulses comprising a sheet of magnetic material, means for passing said sheet between a pair of movable drums each having a spiral path of magnetic wire, a source of signals representative of said sound impulses magnetically coupled with said spiral paths to magnetically record said sound impulses, and means for controlling the amplitude of said sound by a pilot signal located on the marginal zones of said sheet, said means being magnetically coupled to an apparatus for expanding and contracting said sound impulsg.

13. A method of recording or reproducing sound by magnetic `scanning including the steps of drawing a strip of magnetic material through a magnetic ield which is magnetically coupled through a spherical magnetic bearing to a source of signals representative oi' sound impulses, and

means for wiping out said magnetic scanning by passing a current through means for energizing a bar for forming a uniform magnetic field.

14. A magnetic scanning system for recording soimd comprising a long wide sheet of magnetic material having marginal apertures on each side thereof, a plurality of sprockets engaging said apertures for imiformly passing said sheet between a pair of movable drums of nonmagnetic material, a spiral wire of magnetic material secured to each of said drums, means to record said sound by magnetically coupling the spirals of the movable drums with a source 'of signals representative of sound, and a pair of bars forming a constant magnetic iield arranged to wipe out said recordedsound impulses.

GILBERT Il.. CLARK. 

